This invention relates to an improved sewing machine in which the use of a modified handwheel results in improved lubrication, lower machine temperatures, reduced maintenance, and an increased lifetime of the machine's components.
The present invention, although applicable to many types of sewing machines, has proven to be quite effective in connection with an overedge sewing machine of the well-known "Merrow" type illustrated in prior U.S. Pat. Nos. 2,879,733 and 3,958,460. The disclosures of these two U.S. patents are incorporated herein by reference.
In the Merrow machine, a primary drive shaft extends through a housing and has its driven end protruding outwardly of the housing. The protruding end of the shaft carries the handwheel which has a circumferential groove driven by a V-belt. The shaft is journaled in the housing and typically is supported on a needle bearing located near the handwheel. The handwheel is spaced closely to the housing exterior. This spacing prevents thread and debris from entering between the handwheel and the housing, and it also minimizes the lever arm between the pulley groove and the shaft bearing. During normal machine operations, the V-belt drives the handwheel at a high speed, typically about 5500 rpm.
The incidence of failure of the needle bearings in such machines has been greater than desirable. In a previous effort to avert such failures, a lubricant supply passage was connected directly to the needle bearing, but this resulted in excessive oil loss at the exterior of the housing. Now, it has been discovered that a source of the problem was that the high speed rotation of the handwheel in close proximity to the housing caused fluids to be centrifugally propelled radially outward in the space between the handwheel and housing. This centrifugal effect caused air and lubricant to be aspirated along the shaft, inhibiting proper bearing operation and increasing friction. The present invention overcomes this problem and causes the machine to run at cooler temperatures, thereby increasing the comfort of the machine operator and the lifetime of the machine components.